The present invention relates to mine roof anchors and, more specifically, to novel means for retaining a shell, a tapered expansion plug, and a threaded bolt in assembled relationship prior to engagement within a hole in the mine roof.
Mine roofs are commonly supported by plates held in position by the head of a bolt extending into and fixedly retained in an opening drilled for such purpose in the mine roof. One of the most widely used means for retaining the bolt is a so-called expansion anchor, comprising an expansible shell and a tapered plug having an opening in which the bolt is threaded. Since the tapered plug and bolt, although threadedly connected to one another, are not otherwise connected to the shell, it is necessary to provide means for maintaining the elements in properly assembled relation prior to use and during insertion into the hole.
Several different means have been used for the purpose of holding the bolt, shell and plug in the desired relationship. One of the most familiar is a bail or strap attached in some manner to the shell and passing over the end of the plug. This maintains the shell and plug in assembled relationship prior to threading the bolt into the plug. As the assembly is inserted upwardly into the drilled hole, the shell is prevented from falling out of position by engagement therewith of the strap.
Another is the so-called "pal nut" which is threaded on the bolt below the shell, the plug being threaded on above the shell. This is usually a relatively thin or fragile nut which may be twisted or sheared off as the bolt is rotated to pull the plug into the shell and effect expansion thereof. The pal nut does not, of course, retain the plug in assembled relation with the shell, and is not itself attached in any way to the shell. Each item is provided separately and the bolt is threaded through the pal nut and into the plug, with the shell therebetween, at the time when the assembly is to be inserted in the drilled hole in the mine roof. The pal nut merely serves as a stop, preventing the shell from falling down the bolt when inserted upwardly into the hole. The opening in the pal nut is provided with a thread which may be cast, machined or stamped, depending on the type of nut, but in any case the nut has the usual hexagonal outer periphery and, as previously mentioned, is not attached or engaged in any manner with the shell.
The cost of anchor assemblies having straps or bails to maintain the plug and shell in assembled relation is increased by the added labor involved in assembling the shell, plug and bail prior to shipment. Although the cost is less when a pal nut is used instead of a bail, it is more difficult to assemble the separate elements on the bolt when ready for use, and there is a greater possibility of the pal nut being dropped or lost since it is not connected to the shell.
It is a principal object of the present invention to provide a mine roof expansion anchor having novel and improved means for retaining the elements in assembled relation.
A further object is to provide a retaining member for a mine roof expansion shell which is low in cost, yet is engaged with the shell prior to use.
Other objects will in part be obvious and will in part appear hereinafter.